Broccoli in Zone 4a & 4b
Brassica oleracea
When to plant broccoli in zone 4b
Zones 4a and 4b share the same average frost dates in our data, so this page covers both.
Method: Start indoors: Start indoors from seed, then transplant outside. Broccoli needs a head start most zones can't give it by direct-sowing alone.
| Start indoors | Apr 3–Apr 10 |
|---|---|
| Direct sow / transplant outside | May 1–May 8 |
| Estimated harvest | Jul 5–Jul 12 (~65 days after transplanting) |
Spacing: 1 per square foot (square-foot-gardening spacing). Mature height: 1.5-2 ft.
Broccoli is a cool-season crop wearing a warm-season crop's growing calendar in a lot of gardens. Start it too late in spring and heat pushes it to bolt into loose, bitter flower heads before it ever forms a proper crown.
How broccoli fits zone 4's season
Zone 4b's frost-free window runs about 128 days, from May 15 to September 20. Broccoli needs about 65 days from transplant to first harvest.
Good companions
- Onion: Onion scent is reputed to confuse cabbage moths that target brassicas. The research behind this is real but garlic-specific (field trials intercropping garlic with cabbage reduced diamondback moth damage) — onion hasn't been tested the same way, so treat the onion version as a reasonable extrapolation, not a directly measured result.
Where to buy broccoli seeds
See why we recommend these suppliers →
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See it growing
Search YouTube for "growing broccoli" videos → (a live search, not a hand-picked video; results vary and aren't vetted by us)
← Back to the full zone 4b calendar · Full companion planting guide · Full plant profile · Plan your beds in the Garden Designer →
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Growing Broccoli in USDA zone 4b: when to start seeds indoors, when to direct-sow, and when to expect a harvest.
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